Regional Sedimentary Responses to Syndepositional Faulting of Upper Cretaceous Limestones, B Oilfield, Central Iraq

While the syndepositional faults have clear impacts to the sedimentary process of the Upper Cretaceous limestones in central Iraq, their controls on sedimentary patterns during the deposition of different reservoir intervals remain unclear.

Based on analysis of fault activity history and interpretation of sedimentary facies, the regional facies distribution models of the B oilfield in response to fault slips are established. The growth rates of two major faults are 0–25 m/Ma, less than the average production rates of carbonate ramps. Also, the variations of thickness differences between the hanging wall and footwall of the faults are in accordance with that of the growth rates, demonstrating the controls of faults on the stratigraphy. Specifically, the fault activity led to subsidence in the hanging wall and uplift in footwall the within the fault-block, creating local paleo-topographic relief. As a result, high-energy sedimentary facies such as shoals preferentially develop on the footwall, while the facies belts on the hanging wall have greater thickness. By influencing the facies distribution, the syndepositional faulting may also have potential impacts on the distribution of limestone reservoirs, which have larger thickness and better properties at the footwall region.